Vapour recovery systems in a storage tank filling pipe

ABSTRACT

A vapor recovery system for use during filling of a tank installation with a volatile liquid. The tank has a fill-pipe for the introduction of the liquid into the tank wherein the exit to which fill-pipe is normally below the liquid level in the tank. The vapor recovery system includes a reduced cross-sectional area region of the fill-pipe and a duct extending from that region through the side wall of the fill-pipe into the ullage space above the liquid level in the tank. The system further has a valve assembly associated with the duct which valve assembly normally closes off the duct, but which valve assembly is opened by flow of liquid along the fill-pipe into the tank, such that vapor in the tank may be drawn along the duct from the ullage space by the reduced static pressure in the region of reduced cross-sectional area of the fill-pipe. A method of recovering vapor using such a system is also described.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. national stage application of InternationalApplication PCT/GB2003/003284, filed Jul. 29, 2003, which internationalapplication was published on Feb. 5, 2004, as International PublicationWO2004/011363 in the English language. The International Applicationclaims priority of United Kingdom Patent Application 0217673.3, filedJul. 30, 2002.

This invention relates to a vapour recovery system for use duringfilling of a tank for a volatile liquid. The invention further extendsto a tank installation for volatile liquids and including such a vapourrecovery system.

The invention is particularly concerned with tank installations forvolatile liquid hydrocarbon fuels such as petroleum spirit, aviationspirit (or avgas) and diesel fuel, all of which liquid fuels arehereinafter referred to simply as “petrol”. However, the invention couldbe used with tanks for other volatile liquids, where the tank content isperiodically replenished.

In the ullage space above liquid petrol in a tank, there exists amixture of air and petrol vapour. When the petrol is being replenished,the in-flowing petrol is in a state of considerable agitation and thistends to produce yet more petrol vapour. The in-flow of the petrol willdisplace a corresponding volume of vapour and it has been the practicefor many years simply to discharge that vapour to atmosphere.

Environmental, health and safety grounds have recently insisted thatattempts are made to collect the vapour displaced from a tank duringreplenishment of the petrol, and subsequently to condense that vapourback to liquid petrol. Consequently, many modern road delivery petroltankers are equipped with vapour collection apparatus which is connectedto a tank when a delivery is being made and the recovered vapour isreturned to the tanker. Over many deliveries, significant quantities ofrecovered petrol can be involved, all of which represents a loss to thesite operators.

In International Patent Specification No. WO 02/40393 (Molinar Limited)there is described a vapour recovery system intended for use with petroltanks and in which vapour is drawn from the ullage space of a tank by areduced pressure generated by the in-flow of liquid, on replenishing thepetrol in the tank. This system relies on a connection externally of thetank to the fill-pipe and also either independently to the ullage spaceor to that space through a vent pipe to the tank. There is alsodescribed a system for fitting to the fill-pipe within the ullage spaceof the tank but this system cannot give safe operation when no fillingis taking place and petrol is being drawn from the tank, for example tobe dispensed to individual motor vehicles. This is because the ullagespace is in direct communication with the fill-pipe when there is noin-flow of petrol and so both the fill-pipe and the ullage space will beat the same, usually sub-atmospheric, pressure.

A principal aim of the present invention is to provide apparatus for anda method of recovering vapour displaced from the ullage space of a tankduring replenishment of a volatile liquid stored in the tank, whichapparatus and method is integral with the tank and is caused to operateby the in-flow of the liquid, so recovering the condensed vapour intothe tank.

According to a first aspect of this invention, a tank installation for avolatile liquid and having a fill-pipe for the introduction of theliquid into the tank wherein the exit to which fill-pipe is normallybelow the liquid level in the tank, there is provided a vapour recoverysystem for use during filling of the tank which system comprises:

-   -   means defining a reduced cross-sectional area region of the fill        pipe;    -   a duct extending from the region of reduced cross-sectional area        through the side wall of the fill-pipe to open into the ullage        space above the liquid level in the tank; and    -   a normally-closed valve assembly associated with the duct which        valve assembly normally closes off the communication of the        region of reduced cross-sectional area and the ullage space, but        which valve is opened by flow of liquid along the fill-pipe into        the tank, such that vapour in the tank may be drawn along the        duct from the ullage space by the reduced static pressure in the        region of reduced cross-sectional area of the fill-pipe.

According to a second aspect of this invention, there is provided amethod of recovering vapour displaced from the ullage space of a tankinstallation during the introduction of a volatile liquid into the tankthrough a fill-pipe wherein the exit from the fill-pipe is normallybelow the liquid level in the tank, there being a reducedcross-sectional area region provided within the fill pipe, in whichmethod vapour is drawn by a reduced pressure generated in the region ofreduced cross-sectional area of the fill-pipe by the in-flow of liquid,the vapour being drawn through the side wall of the fill-pipe along aduct communicating between the ullage space and the region of reducedcross-sectional area, a normally-closed valve assembly being associatedwith the duct and which normally closes off the communication of theregion of reduced cross-sectional area and the ullage space, which valveassembly is opened by the in-flow of liquid along the fill-pipe into thetank, such that the reduced static pressure in the region of reducedcross-sectional area draws vapour in the tank into the opened duct to beentrained in the in-flowing liquid.

The apparatus and method of this invention seeks to provide a region oflow pressure within the fill-pipe, by virtue of the in-flow of thevolatile liquid. That region of low pressure is connected back to theullage space of the tank, but within the tank itself, such that vapouris drawn from the ullage space to the low pressure region. There, thevapour becomes entrained with the in-flowing liquid and at least somecondensation of the vapour will take place, as the vapour is mixed withthe liquid. Further, by appropriate configuration of the normally closedvalve assembly, adiabatic expansion of the vapour may take place withinthe valve assembly, such that the vapour is cooled and this promotes thecondensation thereof.

In a preferred embodiment of this invention, the vapour recovery systemis formed as an integral unit adapted for fitting to a fill-pipe of atank. The unit may be provided with a connector at each of its two ends,such that a fill-pipe may be parted below the mounting of the fill-pipeto a tank, the unit then being connected to the remaining upper part ofthe fill-pipe and the separated part of the fill-pipe being shortened asnecessary and connected to the lower connector of the unit.Alternatively, the fill-pipe may be removed from a mount therefor, theunit is connected directly to that mount, and the shortened fill-pipebeing connected to the unit.

The duct extending from the region of reduced cross-sectional areapreferably has a first portion which extends from that region (where thereduced pressure is formed), upwardly away from the lower exit from thefill-pipe. The duct may then have a second portion which extends fromthe first portion generally outwardly of the fill-pipe to communicatewith the ullage space of the tank. In such a case, the normally closedvalve assembly may be furnished between the first and second portions ofthe duct and advantageously the first portion of the duct serves as avalve member for the valve assembly. For example, the first portion ofthe duct may be defined by a tube mounted for sliding movement coaxiallywithin the fill-pipe and being spring-urged upwardly to a first positionwhere the valve assembly is closed. Such a tube may be moved downwardlyagainst the spring force under the action of the in-flow of liquid, downthe fill-pipe into the tank.

In order to allow the tube to move and so open the valve assembly, thetube may be fitted with a spoiler and on which the liquid flow may act,to impart a force to the tube. Such a spoiler may comprise a vane,baffle or paddle lying in the liquid flow path along the fill-pipe. Apreferred form of baffle comprises an annular cup surrounding the outersurface of the tube and facing the liquid flow direction.

In one embodiment, the normally closed valve includes a carrier whichalso defines the second portion of the duct and which is opened to theinterior of the tube when the tube moves under the action of in-flowingliquid, but which is closed when there is no in-flow, because the tubewill move back to a rest position under the action of the spring force,so closing the valve. To ensure the second portion of the duct, incommunication with the ullage space of the tank, is closed-off from thetube when there is no in-flow, appropriate seals may be provided betweenthe tube and the second portion. It is important that there is anadequate sealing, to isolate the ullage space of the tank (which will beat a sub-atmospheric pressure as liquid is drawn from the tank) from theinterior of the fill-pipe, which normally will be more or less atatmospheric pressure.

The region of reduced cross-sectional area of the fill-pipe, at which areduced pressure is produced during the in-flow of liquid, preferably isdefined by an insert fitted to the internal wall of the fill-pipe. In acase where the fill-pipe is parted to permit the insertion of a separatevapour recovery unit, the insert may be fitted into the upper end of theseparated part of the fill-pipe, before reassembly of that to the vapourrecovery unit. In an alternative arrangement, the region of reducedcross-sectional area is defined by an element fitted to the end of thefirst portion of the duct, within the vapour recovery unit, nearer theexit end of the fill-pipe. In either case, the insert or element shouldsuitably be profiled to define a venturi within which the speed of theliquid in-flow will be increased, so reducing the static pressure withinthat flow.

By way of example, two specific embodiments of vapour recovery units ofthis invention, and certain modifications thereof, will now be describedin detail, reference being made to the accompanying drawings, in which:

FIG. 1 is a diagrammatic vertical section through an undergroundforecourt petrol tank as installed at a petrol station for dispensingpetrol to motor vehicles, which tank is fitted with the first embodimentof vapour recovery unit of this invention;

FIG. 2 is a detailed view on an enlarged scale of the vapour recoveryunit fitted into the fill-pipe, but with the valve assembly in a firstposition;

FIG. 3 is a horizontal sectional view through the unit of FIG. 2 takenon line II-III marked on that Figure;

FIG. 4 is a view similar to that of FIG. 2 but with the valve assemblyin a second (opened) position;

FIG. 5 is a detail of part of the valve assembly of FIGS. 2 and 4;

FIGS. 6 and 7 are sectional views through the second embodiment ofvapour recovery unit and respectively in closed and opened positions;and

FIGS. 8 and 9 show modifications of the tube used in the units of FIGS.2 to 4 or FIGS. 6 and 7.

Referring initially to FIG. 1, there is shown diagrammatically anunderground bulk petrol tank 10 provided with a manhole fitted with acover 11 to which is mounted a fill-pipe 12, communicating through aT-connector 13 to a horizontal pipe 14 leading to a fill locationwhereat a road tanker may connect to the pipe 14 for a bulk delivery ofpetrol, to replenish the liquid in the tank 10. A vent pipe 15communicates with the ullage space 16 within the tank 10, above thelevel 17 of liquid petrol 18 within the tank. The lower end 19 of thefill-pipe 12 is disposed below the level 17, for all normal operation ofthe tank. Such an arrangement is essentially conventional.

A vapour recovery unit 21 is fitted into the fill-pipe 12, immediatelybelow the cover 11 and so within the ullage space 16 of the tank. To fitthe unit 21, the fill-pipe is removed from a nipple screwed into thecover 11 and to the upper part of which is threaded the T-connector 13.The removed fill-pipe is shortened as necessary, and is connected to thelower end of the vapour recovery unit 21. The upper end of the unit 21is then attached to the lower part of the nipple, below the cover 11, bymeans of interengaging threads. In addition to or instead of thosethreads, a securing bolt 22 may be provided, which bolt is threaded intoan upper part of the unit 21 and extends out of the upper end of theT-connector 13, a suitable seal and fastening arrangement being providedfor the bolt 22, externally of the connector. The bolt may be hollow toallow pressure measurements to be performed externally of the tank, toensure that the vapour recovery unit 21 is operating satisfactorilyduring the in-flow of petrol.

Referring now to FIGS. 2 to 5, the vapour recovery unit 21 is shown inmore detail. This unit comprises a cylindrical shell-like main body 24having external threads 25 at its upper end 26, for interengagement withthe internal threads of the cover nipple. A three-armed spider 27 isprovided within that upper end 26 and carries a central boss 28 providedwith an internally threaded bore 29 with which bolt 22 is engaged. Thearms 30 of the spider 27 are extended downwardly below the upper end 26,within a central region of the main body 24. In this central region, thearms are hollow, as best seen in FIG. 3, so as to give communicationbetween the exterior of the unit 21 and the bore through the boss 28.

The boss 28 is extended downwardly below the arms 30 and so into thelower region 31 of the unit. A tube 32 is slidably mounted within thisdownward extension 33 of the boss 28, which tube may thus slidecoaxially within the main body 24. Above the lower end of the boss 28,there is provided an internal shoulder 34 (FIG. 5) and the upper end ofthe tube 32 has an outwardly-projecting lip 35, a helical compressionspring 36 encircling the tube and acting between the shoulder 34 and lip35. In this way, the tube 32 is spring-biased upwardly to the positionshown in FIG. 2, but may move downwardly against the action of thespring 36, to the position shown in FIG. 4.

Upward movement of the tube is limited by lip 35 engaging thethree-armed spider 27 at the upper end 26 of the main body 24. Downwardmovement of the tube 32 is limited by binding of the turns of the spring36. A cup-shaped baffle 38 is provided on the tube 32, immediately belowthe downward extension 33 of the boss 28, when the tube is in theposition shown in FIG. 3, that baffle moving away from the extension 33when the tube moves to the position shown in FIG. 4.

Both ends of the tube 32 are open and a seal ring 39 is provided belowthe three-armed spider 27 in the upper end 26 of the main body 24, suchthat when the tube is in the position shown in FIG. 2, the lip 35 willseal against the ring 39. A further seal ring 40 is provided between thebaffle 38 and the lower end of the downward extension 33, so that anadditional seal is formed here when the tube is in the position shown inFIG. 2. Movement of the tube downwardly to the position shown in FIG. 4opens the communication between the hollow arms 30 and the interior ofthe tube 32, so giving communication between the ullage space of thetank, external to the fill-pipe, and the interior of the fill-pipe,below the tube 32. Return of the tube to the position shown in FIG. 2closes off that communication and so isolates the ullage space from theinterior of the fill-pipe below the vapour recovery unit 21.

The lower end 41 of the main body 24 is externally threaded so that theremaining part of the fill-pipe, following its removal from the covernipple and appropriate shortening and threading, may be connectedthereto. Within the lower part, there is provided an insert 42 whichserves to reduce the cross-sectional area of the fill-pipe, the insertbeing profiled so as to define a venturi within the fill-pipe.Liquid-flow through that venturi will thus be of an increased speed, soreducing the static pressure within the venturi. The lower end of thetube 32 is exposed to that reduced pressure, during in-flow of liquid.

In operation, the in-flow of liquid along pipe 14 and then through theunit 21 into the fill-pipe 12 will generate a region of low pressurewithin the venturi-like insert 42. The in-flow of the liquid willimpinge on the cup-like baffle 38, so moving the tube 32 downwardlyagainst the action of spring 36. This opens the communication betweenthe interior of the tube and the hollow arms 30, whereby the reducedpressure within the tube 32 will draw vapour into those hollow arms,from the ullage space of the tank. That vapour is carried downwardlythrough the tube 32 into the in-flowing liquid, to be entrained withthat liquid and returned as at least partially condensed liquid, to thetank.

Referring now to FIGS. 6 and 7, there is shown a second embodiment whichoperates on much the same principles as that described above, and so theinstallation within a fill-pipe will not be described in detail here. Inthis embodiment, a four-armed spider 50 is provided within the main body51 of the unit, each arm being hollow and communicating through thecylindrical wall of the main body to the ullage space of the tank. Asshown in FIGS. 6 and 7, the upper end of the spider 50 is closed offwith a screw-threaded cap 52 though a bolt and pressure tapping may beemployed, as with the embodiment of FIGS. 1 to 5. A housing 53 isprovided below the spider 50, a valve member 54 being slidably mountedwithin that housing for movement coaxially within the fill-pipe. Thevalve member has a head 55 which is a snug fit within the housing 53 andis spring-urged into engagement with the underside of the spider withinthe housing, a seal ring 56 being provided on the spider to effect aseal to the head when urged against the spider. The stem 57 of the valvemember is hollow and apertures 58 are provided adjacent the head of thevalve member, to communicate with the hollow stem. A plurality ofrelatively small through-bores 59 are formed in the head 55, on agreater pitch circle than the diameter of the seal ring 56, wherebyliquid flow may take place through those bores 59 and into the stem 57,through the apertures 58, when the head has moved away from the spider.

As with the first embodiment, the stem 57 of the valve member isprovided with a cup-shaped baffle 60 below the housing 53 and within thelower part of the main body 51 of the unit. Also, an insert 61 isprovided within the lower part of the main body, to reduce the flowarea.

When there is no in-flow of liquid along the fill-pipe 12, the valve isin the setting shown in FIG. 6. The head 55 engages the seal ring 56 andprevents communication between the hollow arms of the spider 50 and thehousing 53. When there is liquid flow downwardly along the fill-pipe,the baffle 60 serves to move the valve member 54 against the action ofthe spring, so moving the head 55 away from the seal ring 56 and openingcommunication between the ullage space of the tank and the lower end ofthe hollow stem, through the arms of the spider and then through thebores 59 in the head 55 and into the apertures 58. As the through-bores59 are of relatively small diameter, there will be adiabatic expansionof the vapour passing therethrough, which will cool the vapour sotending to condense it, to liquid petrol.

As an alternative to providing an insert within the lower part of themain body of the vapour recovery unit, or within the upper part of thefill-pipe which is attached to the lower part of the main body, thelower end of the tube 32 (or of the valve stem 57 in the case of thesecond embodiment of FIGS. 6 and 7) may carry a profiling element whichserves to reduce the flow area within the fill-pipe. Two possibilitiesfor such profiling elements are shown in FIGS. 8 and 9. The element 64of FIG. 8 comprises two conical shapes arranged base-to-base whereby theflow is accelerated on passing the upper conical shape and is slowedagain, on passing the lower conical shape. The element 65 of FIG. 9 hasa more rounded profile but still serves to produce a venturi-like effectwithin the fill-pipe, in the lower region of the vapour recovery unit.

1. A tank installation for a volatile liquid wherein there is an ullagespace above the liquid in the tank in which said ullage space vapourcollects, said tank installation having a fill-pipe for the introductionof volatile liquid into the tank, said fill-pipe having an exit which isnormally within said liquid in the tank, and a vapour recovery systemfor use during filling of the tank to recover vapour displaced from saidullage space, said vapour recovery system comprising: restriction meanswithin the fill-pipe defining a region of the fill-pipe of reducedcross-sectional area whereby in-flow of liquid along the fill-pipe intothe tank results in a reduced static pressure in said region; a ductextending from said region of reduced cross-sectional area through thefill-pipe to open into said ullage space above the liquid in the tank;and a normally-closed valve assembly associated with the duct whichvalve assembly normally closes off communication through the ductbetween said region of reduced cross-sectional area and said ullagespace, said valve being opened by in-flow of liquid along the fill-pipeinto the tank, such that vapour in the ullage space is drawn from theullage space along the duct by the reduced static pressure in the regionof reduced cross-sectional area of the fill-pipe.
 2. A vapour recoverysystem as claimed in claim 1, wherein the duct has a first portion and asecond portion, said first portion extending from the region of reducedcross-sectional area of the fill-pipe upwardly away from the exit of thefill pipe, and said second portion extending from the first portiongenerally outwardly of the fill pipe to communicate with the ullagespace of the tank.
 3. A vapour recovery system as claimed in claim 2,wherein the normally-closed valve assembly is formed between the firstand second portions of the duct.
 4. A vapour recovery system as claimedin claim 2, wherein the first portion of the duct is defined by a tubemounted co-axially within the fill-pipe, the lower end of said tubebeing in the vicinity of the region of reduced cross-sectional area ofthe fill-pipe.
 5. A vapour recovery system as claimed in claim 4,wherein the tube is mounted for sliding movement co-axially within thefill-pipe, the tube forming a part of the normally-closed valve assemblyof the vapour recovery system.
 6. A vapour recovery system as claimed inclaim 5, wherein a spring applies a spring-force to the tube to urge thetube upwardly to a first position where the valve assembly is closed,and the tube is moved downwardly against the spring-force under theaction of the in-flow of liquid, down the fill-pipe and into the tank.7. A vapour recovery system as claimed in claim 6, wherein the tube isfitted with a spoiler, said spoiler lying in the liquid in-flow alongthe fill-pipe whereby the in-flow of liquid acts on the spoiler and somoves the tube downwardly against the spring-force.
 8. A vapour recoverysystem as claimed in claim 7, wherein the spoiler projects into theliquid in-flow and is selected from the group consisting of a vane, apaddle and an annular cup surrounding the tube.
 9. A vapour recoverysystem as claimed in claim 5, wherein the tube is mounted in a carrierwhich defines the second portion of the duct, the second portion of theduct being opened to the interior of the tube when the tube moves toopen the valve assembly.
 10. A vapour recovery system as claimed inclaim 9, wherein the tube is provided with a head adjacent the carrier,said head being provided with a plurality of relatively small holesthrough which vapour passes on being drawn from the second portion ofthe duct to the first portion thereof, whereby the vapour is expandedand cools promoting the condensation thereof.
 11. A vapour recoverysystem as claimed in claim 9, wherein a seal is provided between thetube and the carrier, said seal sealing the second portion of the ductfrom the interior of the tube when valve assembly is closed.
 12. Avapour recovery system as claimed in claim 11, wherein said sealincludes a first seal member arranged to seal off the upper end of thetube from the second portion of the duct when the valve assembly isclosed.
 13. A vapour recovery system as claimed in claim 12, whereinsaid seal includes a second seal member arranged to seal the exteriorsurface of the tube to the carrier, at least when the valve assembly isin its normally-closed setting.
 14. A vapour recovery system as claimedin claim 9, wherein the carrier defines three second duct portions eachextending generally outwardly from a central region of the carrier tothe outer surface of the fill-pipe.
 15. A vapour recovery system asclaimed in claim 1, wherein the region of reduced cross-sectional areaof the fill-pipe is defined by an insert, said insert being fittedinternally of the fill-pipe.
 16. A vapour recovery system as claimed inclaim 2, wherein the region of reduced cross-sectional area of thefill-pipe is defined by an element fitted to an end of the first portionof the duct, said end being nearer the exit of the fill-pipe.
 17. Avapour recovery system as claimed in claim 1, wherein the region ofreduced cross-sectional area of the fill-pipe defines a venturi, whereinthe speed of liquid in-flow is increased on passing through the venturi.18. A vapour recovery system as claimed in claim 1, wherein the systemis formed as a separate integral unit adapted for fitting to a tankfill-pipe.
 19. A vapour recovery system as claimed in claim 18, whereinthe separate integral unit has two ends each of which is provided with arespective connector, and the fill-pipe has an upper section connectedto one connector of the integral unit, and a lower section connected tothe other connector of the integral unit.
 20. In a tank installation fora volatile liquid and having a tank with an ullage space above liquid inthe tank wherein vapour from the liquid collects, said tank installationhaving a fill-pipe for the introduction of volatile liquid into thetank, said fill-pipe having an exit which is normally within the liquidin the tank, and a vapour recovery system for use during filling of thetank to recover vapour displaced from said ullage space as the volume ofliquid in the tank increases, there being a region of reducedcross-sectional area provided within the fill pipe, a method ofrecovering vapour comprising: generating a reduced static pressurewithin the region of reduced cross-sectional area by the in-flow ofliquid along the fill-pipe; drawing the vapour along a duct entering thefill-pipe so as to communicate between the ullage space and the regionof reduced cross-sectional area, by virtue of the reduced staticpressure at said region; and normally closing-off said communication ofthe ullage space with the region of reduced cross-sectional area by anormally-closed valve assembly associated with the duct, which valveassembly is opened by the in-flow of liquid along the fill-pipe into thetank during the filling thereof, such that the reduced static pressurein the region of reduced cross-sectional area during filling of the tankdraws vapour from the ullage space in the tank into the opened duct tobe entrained in the in-flowing liquid.